This invention relates to a solution of the problem of control of the instant of ignition, and thereby the ignition angle, measured in relation to a fixed reference point in time, usually top dead center in an internal combustion piston engine. The solution of this problem is important, not only in the context of satisfactory functioning of the internal combustion engine, but also for decreasing the proportion of noxious substances in the exhaust gases of the engine.
One known approach to the solution of this problem operates digitally thereby avoiding additional mechanical adjustment elements, such as centrifugal governors. This approach, disclosed in U.S. Pat. No. 3,696,303 utilizes two pulse trains which are produced synchronously with the periodic revolutions of an element of the internal combustion engine. These two pulse trains are generated by means of a rotating toothed disk. The pulses of one pulse sequence are stored during a predetermined time interval so that, at the end of such time interval, there is stored (as an integration reault in a counter) a pulse number which is proportional to the speed of revolution of the engine. The pulses of the second pulse sequence, likewise synchronous with the rotation of the element of the engine, are counted and stored until a predetermined sum value is attained for the two stored pulse numbers. As soon as this predetermined sum value is attained, the known method produces an accurately timed ignition signal.
With this known method, it is not feasible, at least without considerable expenditure, to achieve a non-linear functional relation between the ignition angle and the speed of revolution of the internal combustion engine. This disadvantage is avoided by a method in accordance with the invention which is characterized in that the predetermined interval is a constant angle interval extending between a first and a second marking, and in that the electric quantity and/or the integration constant of the integrator is varied speed-dependently to achieve a non-linear dependence of the ignition angle on the speed.
A first essential characteristic of the invention may be found in the fact that unlike the state of the art dealt with above, it does not use a constant time interval, but rather uses a constant angle interval. Accordingly, the integration result is inversely proportional to the specific speed of the engine. If a digital arrangement, i.e., an arrangement operating with pulses, is used to execute the method in accordance with the invention, the rotating element of the engine need not be supplied with means for pulse generation, such as teeth, but only with markings defining the constant angle interval. Another characteristic, made possible only by the first essential characteristic, consists in that, generally speaking, the integration process during the constant angle interval is controlled as a function of engine speed. In an analog method in accordance with the invention, the integrator is controlled by an electric voltage whose amplitude is varied for given speed values. Moreover, it is also possible to obtain by means of these given speed values (which would have to be rapidly determined, e.g., by means of a tachometer) the signals to switch the integration constant of the integrator within the integrator circuit.
Another possibility of the method in accordance with the invention provides that the integrator is a pulse counter and operates on a pulse train produced outside the engine whose frequency is modified as the number of pulses within the angle interval increases. Accordingly, as soon as the pulse number stored in the pulse counter during the fixed angle interval attains a given value, switching to a higher frequency occurs. The position and the extent of these sudden changes of frequency or frequency steps determines the non-linear function by which the rotational speed influences the ignition angle. In the final analysis, an approximation of the non-linear shape of this curve is a polygon.
As a rule, the optimum ignition angle is a function, not only of the speed of revolution of the engine, but is also a function of the engine load. This load dependency can be taken into account in accordance with the invention by taking the difference between the integration result and a load-dependent signal, and producing the ignition signal when the difference assumes a given value. To this effect, following termination of the angle interval, the integrator can be discharged at a constant rate which is independent of the rotational speed, and the ignition signal can be generated on comparison of the storage value of the integrator with the load-dependent signal. This variant of the method in accordance with the invention is likewise applicable for an analog as well as digital embodiment for practicing the method. The speed-independent time constant can be achieved, e.g., in a digitally operated embodiment, by causing the pulse counter to count pulses of a constant frequency in a backward counting direction.
As we have seen, taking into account the functional relation of the ignition angle and the speed of the engine, the invention provides for an approximation of the non-linear shape by a polygon curve. In accordance with a further development of the invention, the correction required by the effect of engine load on the optimum ignition angle is made by providing a load-dependent signal which is modified in steps by a load sensor. Each of the steps causes a modification of the adjustment of the ignition angle by the same value. In this effect, an additional integrator can be controlled in the angle interval by a further electric quantity and the latter and/or the integration constant can be modified by a load sensor. In such a case, the integration result of the second integrator at the end of the angle interval is used as a load-dependent signal. Here again, the method can be executed with simple means by both an analog and a digital arrangement. For example, in an analog solution, the second integrator is controlled by an additional electric voltage, the amplitude of which is varied for given load values. Moreover, the additional integrator can also be an additional pulse sequence generated outside the engine whose frequency is modified when given load values are reached within the angle interval. These sudden changes in frequency occur, as in the case of the frequency changes produced by engine speed changes, to produce an actual ignition angle-engine load curve formed of straight line segments whhich approximates the ideal shape of the curve of the functional relation of the ignition angle and the engine load.
The arrangement in accordance with the invention for execution of the method, independent of whether the arrangement functions analoguely or digitally, is characterized in that the rotating element of the engine is provided with two markings angularly displaced to define the angle interval. The position of the markings are defined in relation to the positions of the element at a given operating phase of such element which, for a piston engine, is preferably at top dead center. With the engine running, the markings pass the stationary receivers or pick-ups designed as proximity switches in a time interval inversely proportional to the rotational speed. In this way, control signals are generated in the pick-ups for the connected integrators which are provided in a number and arrangement determined by the number of different ignition points of the engine. At this point, it becomes quite clear that the invention avoids pulse-generating elements, e.g., a toothed disk, driven by the internal combustion engine. Rather, it is merely necessary to provide markings on a rotating element of the engine which, while rotating, pass stationary pick-ups. As these markings pass these stationary pick-ups, they produce pulses or signals which, in turn, initiate or terminate the delivery of electrical quantities to the integrators. The markings can be obtained in a simple manner by local modifications of material, e.g., pins or holes, in the rotating element of the engine. For example, the markings can be provided on the flywheel of the engine while the pick-ups are located on the gear box flange and on the crankcase of the engine. Suitably, the markings and the pick-ups will be arranged on the same radius. The fact that only a small number of markings is required, two markings are sufficient to define the constant angle interval, makes unnecessary a reconstruction of available engine parts in order to form the markings. Nor need there be provided any additional moving parts, such as a toothed disk. This is all the more true because the markings, such as indicated above, can be obtained in a simple manner by local material modifications.
In accordance with the preferred embodiment of the invention, the aforementioned two markings are arranged, insofar as a piston engine is concerned, 80.degree. and 40.degree., respectively, before top dead center in relation to the pick-ups. The number and the arrangement of the pick-ups will depend upon the number of ignition points of the engine. In a four cylinder engine in which two cylinders each are fired simultaneously, two pick-ups will be arranged offset by 90.degree. with respect to top dead center and 180.degree. with respect to each other. In such a case, the markings are associated with each pair of simultaneously firing cylinders.
It may be advisable to include a third marking on the rotating element such that, in case of failure of the other parts of the arrangement, an emergency ignition is brought about, e.g., in a piston engine in top dead center.
A plurality of embodiments for execution of the method in accordance with the invention can be employed. Therefore, the invention is not to be construed as limited to the particular digitally functioning preferred embodiment disclosed.
This preferred embodiment of the invention is characterized in that an oscillator with constant frequency is connected to a first network which steps up or steps down the frequency of the pulses produced by the oscillator. The network feeds a first pulse counter and also receives from it switching signals for producing frequency modifications on attainment of the given pulse numbers. After switching initiated by the control signal produced by the second marking pulses with a constant gating frequency are delivered to the first pulse counter for the purpose of gating the integration result over the first network at a constant rate.
Pulse generation is obtained here by means of oscillators, e.g., a quartz oscillator, so as to ensure the desired precision of the ignition timing within a wide temperature range and over long periods of operation. Mechanical parts subject to wear and tear are avoided, especially since the cooperation of markings and pick-ups occurs without mechanical contact, but merely by the proximity of the markings from the pick-ups.
The modification of the frequency of the pulses delivered to the pulse counter to achieve speed dependence is obtained in a simple manner by switching within the network. These switchings are suitably obtained by electronic switches of known construction.
The influence of the engine load on the optimum ignition angle is achieved by connecting a second network to the oscillator for stepping up or stepping down the frequency of the pulses produced by the oscillator. The second network receives switching signals from the load sensor for producing the frequency variations at the given load values. On the output side, the second network is connected with a second pulse counter. Both pulse counters feed a comparator circuit which produces an ignition signal whenever the integration result in the first pulse counter had been modified to a value which is a function of the load-dependent signal. Accordingly, pulse generation for speed dependence and load dependence occurs in one oscillator and two networks are provided to derive from this single generated pulse frequency the different frequencies required both for achieving rotational speed dependence and load dependence.
In one embodiment of the invention which was tested, an oscillator with a frequency of 1 MHz was found to be useful. The influence of engine speed change on ignition angle is achieved by providing three switchings, namely, at approximately 4000 rpm to 200 kHz, at approximately 1550 rpm, to approximately 500 kHz and at approximately 1150 rpm to approximately 830 kHz. The influence of engine load change on ignition angle is achieved by providing ten steps of 12.5 kHz each. Each frequency step causes a modification of the firing angle by 1.degree. crankshaft angle.
Furthermore, the preferred embodiment of the invention is designed such that the second marking switches the first pulse counter to count backward (for the pulses with the gating frequency) and the comparator circuit produces the firing signal on equality of both pulse counter states. It is possible as a matter of principle to undertake upwards counting with the first pulse counter after completion of the constant angle interval. In this embodiment of the invention, the circuits become especially simple.